As is well known in the aircraft gas turbine engine art, the combustor and associated transition ducts are typically fabricated with a liner that includes means for cooling the liner and for providing protection against thermal stresses. The type of liner that is the concern of this invention is that type that includes an outer cylindrically shaped shell and a plurality of circumferentially spaced segmented panels that are discretely attached to the shell.
This type of construction is exemplified in U.S. Pat. No. 4,302,941 granted to T. L. DuBell on Dec. 1, 1981 entitled "Combustion Liner Construction for a Gas Turbine Engine" and attachment means are exemplified in U.S. Pat. No. 4,512,159 granted to R. L. Memmen on Apr. 23, 1985 entitled "Clip Attachment" both of which are assigned to United Technologies Corporation, the assignee of this patent application. Liners of the type described in these patents are referred to as Floatwall liners since the panels are adapted to displace axially and circumferentially in response to thermals of the system.
It should be understood that the entire combustor and transition duct may utilize Floatwall liners or either one or the other may utilize this type of construction. In this preferred embodiment the invention will be described in conjunction with the transition duct and is particularly directed to means for curing a problem that had plagued the heretofore known transition ducts utilized in certain gas turbine engines. In particular, existing transition ducts were evidencing a problem with the rear Floatwall panel lug which was wearing completely through the support mechanism or backbone of the transition duct as a result of vibratory and thermal motion interaction. This problem was acerbated because the panel is constructed such that there is only a small contact area between the aft Floatwall lug and the transition duct backbone surface. As a consequence, this wear allows the Floatwall panel to have more motion in the airstream causing progressive wear and loosening at the front panel lug, clip and backbone interface.
Lifting of the Floatwall panel allows hot gases from the engine's gas path to recirculate under the Floatwall panel side edges and cause overheating, blistering and cracks locally on the transition duct backbone. Further wear and loosening of the front Floatwall panel lug attachment has the potential of liberating a floatwall panel into the engine gas path with possible damage to the turbine.
Unsuccessful attempts to find a solution to this problem were made prior to this invention. One such attempt was coating the portions of the transition duct, as for example, the inner rear skit portion of the backbone, in order to prevent the lug from wearing through the backbone. Not only was this attempt unsuccessful, it, in fact, accelerated the wear on the lug contact surfaces. Other types of clips were fabricated and also were tested with unsatisfactory results.